Assuming Extreme Grid Transparency, what's the next issue?

[James Parkin]

Let's say one was to design a reactor with a high, (but not exactly 100%) grid transparency. What would the next set of issues be and how would you over come them?

James

[Chris Bradley]

This has been answered many times before in as many different ways, but as I had sympathy for new readers before the forum change, now it is plain all out diabolical. (You can test out how bad it is at the moment by trying to do a 'search' for the following thread. It simply doesn't come up. And, no, if you search for 'FAQ' it only lists a half of all the faqs. Someone wanna try explain why this following link doesn't appear if you do a search for 'FAQ'?)

In view of that, I link you to the last post I'm aware of that was made on this topic:

viewtopic.php?f=14&t=6973

Bottom line is ... an 'issue' to what? I've never seen any evidence for why the 'grid' limits the fusions in a fusor. It seems to be only from 'hot air' expounded by pure idealists that this idea has taken currency. On the contrary, the grid is the 'enabler', not the 'limiter', because without it you would not be able to drive the fusor into the near-coronal discharge regime right at the lowest pressure, thus highest voltage, of the gas discharge region of operation. How else would you be able to initiate ion production, thus discharge, at a central cathode if it weren't for the physical characteristics of a grid with a tight radius wire?

AFAIK: Farnsworth's first idea was no negative grid, but instead a positive grid that causes a central charge accumulation by electron multipaction (excited by an HF outer bias grid), but this resulted in no detectable fusions. Then he ran a negative grid below the discharge level with ion guns. That didn't produce fusions either. The grid for discharge was a 'Hirsch' innovation, I guess because he just got fed up with not seeing any fusions and wanted to see if the whole idea would work if there was a central negative charge at all.

I am now, personally speaking, almost completely convinced that more than 90% of all fusions in a regular fusor are simply beam-target type fusions in the outer shell. The 'beam' particles make it to the shell because they are fast neutrals, formed at the centre of the fusor (more free electrons to grab, right there, maybe). This is why neutron anisotropy appears around a working fusor - because it depends how close the detector is to one of those particular beam-target sites in the shell. Particles in the 'beams' miss the grid, because it is in the nature of the grid that the electric fields will quickly 'kill' ions if they are not correctly lined up to shoot by without loss. On average, ions only have to miss the grid a dozen times before they will collide in a charge exchange and end up as a fast neutral that can then fuse with interstitial deuterium in the shell. The alignment to miss the grids would be far more critical if it needed to miss the grid billions of times to collide with a gas particle, or quadrillion times to collide with another ion, so I think on the balance of likelihood these two latter scenarios are very rare.

[Richard Hull]

I tend to agree with Chris on his exposition. The grid is a non-issue for the fusor, as built here.

To restate the obvious, in simpler terms; no fusor and certainly not the simple fusor, will ever be able to be boosted by one single order of magnitude in fusion power output....No matter by what artifice or expenditure will the fusor ever obtain a power in to power out ratio better than a 100,000 to 1 net loss of energy!

Here endth the lesson.

Suggestion: Build a fusor with any ideas you think are world beaters and prove me wrong. Of course, we know that will never happen.... Not necessarily because you are not capable and maybe not because you don't have cool ideas, but definitely because the nuclear physics involved with the device won't allow it.

Many of us here at fusor.net have already shown that doing fusion is very, very easy. However, with billions of the money spent over the last 60 years, many greater minds have succeeded in showing us that successful net power fusion which is distributable is thus far, totally impossible. So, don't think you are going to find any energy solutions or even energy improvements here. 10 million times more energy input from the wall outlet than net fusion energy output is about the best most here ever do.

Richard Hull

[Dan Tibbets]

Transparent central cathode grid is a primary consideration of the Polywell, where the cathode is "virtual" with an effective transparency of ~ 99.99%. If the neutron production i n WB6 was acurate, the vast majority of fusions were presumably beam beam, or at least beam neutral gas collisions. That beam target fusions occur in Fusors is certain, that they dominate is questionable. There are confusing results with D-D and D-T fusions. In at least one study the D-He3 fusions seemed to occur frequently with embeded fuel in the wire cathode. D-D fusion seemed to dominate in the core. This intrepratation of course depends on your perspective. If you are talking about total fusions then the shell may dominate. But if you are taling about fusion per unit of area there are Japanese studies that suggest 10-50 % of total D-D fusions occur in the core, and the per unit fusion rate in the small core would thusly greatly dominate over any other area.

The question of which is the next step if a transparent grid was possible would seem to be something like the Wiffleball effect and/ or greater central confluence. The opaque grid would certainly impead the energy balance do to loss of KE with grid collisions, unless the occurance of beam- target fusion here was greatly dominate. With transparency the ions converging towards the center could be enhanced, and this has implications for increasing beam- beam interactions. Effectively this detracts from any beam target interactions (which may be good from an energy balance perspective) and also effectively increases the core density and thus contribution of core fusion as a percentage of overall fusion. Things become mixed up, but core collisions weather Coulomb of fusion do not add much to the angular momentum of the ions ( all directions/ bounces are radial from the center). This along with a potential well- transparent cathode grid allows for possibly many more passes through the core. This saves energy and thus helps Q.

But, for fusion power, not only does there need to be good efficiency (many passes) there there needs to be higher density locally ( through significant confluence) or general average density. The Wiffleball effect applies to this claimed greatly increased density (among other efficiency effects).

The Elmore Tuck Watson idea to create a virtual (transparent) central cathode addresses the ion grid transparency issue, but at the cost of not having a fairly opaque electron intercepting grid.The solution to this is to insulate the electron accelerating grid (anode) magnetically. Thus the trials and tribulations of several approaches, including the Polywell, which I am a Fanboy of.

Another way of putting it is that with a fairly opaque cathode grid that the ions hit at high KE, the fusion rate may depend significantly on the beam- target (grid embedded deuterium or Helium3). If so, the fusion rate is near it's maximum. Even with contribution of Beam - beam or beam- background contributions the ratios would be similar. More input energy and or density would increase fusion but only to the point where the grid melted or sputtering polluted the system. If the grid is glowing red you are near your maximum obtainable fusion. Cooling the grid might help, but only a small amount. You are up against a wall. The only way to increase fusion rate much past this limit is to increase transparency of the grid. Either that or increase grid/ fusor size to many , many meters diameter. That could increase yield, but transparency would still be limiting. This applies both to obtainable Q and raw fusion numbers.

Dan Tibbets

[Steven Sesselmann]

I am now, personally speaking, almost completely convinced that more than 90% of all fusions in a regular fusor are simply beam-target type fusions in the outer shell.

Chris, this is an interesting twist on the saga, can you think of an experiment to validate this?

Steven

[Chris Bradley]

Yes. Test for anisotropic neutron emissions in the 'near field', and figure out how far out you need to get before the anisotropy drops below a measurable level (i.e. where it becomes a 'far field' neutron emission - i.e. where the source appears as a point source). If you like, you could back it up with some Monte Carlo type simulations to see what predictions you get for anisotropy at different distances for different assumptions about the neutron sources.

Anisotropy suggests it is shell-bound fusions because;
if it were beam on beam, the reactions would be central so that the neutron emission would appear to come from the centre, thus isotropic at a modest distance, or
if it were beam on wire grid, the reactions would be central so neutron emission would appear to come from the centre, thus isotropic at a modest distance, or
If it were beam on background gas, the point at which ions have picked up enough KE to fuse at a decent rate is as they get to the centre, thus the reactions would be central and isotropic emissions would be measurable at a modest distance.

So anisotropy, as far out as you can detect neutrons, suggests to me that you're looking at shell-bound sites of fusion. The only way* a positive nucleus gets to make it up the electric field gradient to where it is 'more positive' and still have its full acceleration energy is if it's firstly been neutralised whilst at that high KE.

*(Conceivably, if negative ions were being produced at the centre, then this could be another source of high energy ions at the shell. However, as a fusor is a fairly ordinary discharge device, AFAIK I think it is unlikely negative ions are being produced. - If anyone's got experience to make a good argument to say how and if negative ions are produced, I'd be interested to hear it.)

The experiment, then, would be accurate (implies need a consistent reaction rate) anisotropy measurements at different distances (in a device where other causes of anisotropy have been controlled for), and preferably with some post test Monte Carlo analysis to see if the data fits predictions.

[Steven Sesselmann]

Chris,

This theory does not fit well with my ideas on the electric potential of matter, but that doesn't mean its wrong. There are three possible outcomes.

a) Neutrons are produced inside the grid by beam on beam collision
b) Neutrons are produced on the grid by beam on target fusion
c) Neutrons are produced at the shell by fast neutrals

AFAIK some detailed measurements were done by the University of Wisconsin, might be worth revisiting those results. Joe Khachan's team at the University of Sydney also studied the velocities of neutrals coming from the centre.

Steven